The present invention concerns an optical device using semiconductor and, more in particular, it relates to a laser device and an optical waveguide stripe device using a semiconductor material or an integrated optical semiconductor device integrating them.
Semiconductor lasers that have been generally used in various industries such as optical communication or optical recording have been demanded to have high performance, particularly, high speed operation at a reduced cost along with starting an increase in the transmission capacity in the optical communication by the development of the Internet particularly in recent years. As lasers that are advantageous for reducing the cost, a ridge waveguide laser of a simple manufacturing process has been known. Such an example is shown, for example, by T. Fukushima in IEEE Photonics Technology Letters, Vol. 5, No. 9, 1993, pp. 963-965. FIG. 2 shows an example of a cross sectional view of a ridge waveguide laser. As shown in the cross sectional view of FIG. 6, a lower cladding layer, an active layer containing an SCH layer and an upper cladding layer are successively grown in a stacked structure, and the upper cladding layer is removed leaving a mesa stripe by selective etching. In FIG. 6, are shown an n-InP substrate 1 which also serves as a lower cladding layer, an n-InGaAsP guide layer 2, an InGaAsP multi-quantum well active layer 3, a p-InGaAsP guide layer 4, a p-InP upper cladding layer 5, and a contact layer 6 for ohmic connection with an upper electrode 8. For the contact layer, InGaAs lattice-matched with the InP substrate is used. Reference numeral 7 denotes an SiO2 insulation film that electrically insulates semiconductors 4, 5 and the upper electrode 8 in an area other than the contact layer 6 and current flows through the contact layer to the active layer. Reference numeral 9 denotes a lower electrode. Since the ridge semiconductor laser can be manufactured by crystal growth for once, costs therefor can be reduced compared with existent buried type semiconductor lasers that require two or three steps of crystal growing.
A first subject of this invention is to provide a configuration capable of decreasing parasitic elements and attaining a high-speed response in a ridge waveguide laser. A second subject is to provide a configuration having a high reliability in a ridge waveguide laser with reduced parasitic elements.
The first and the second subject described above can be attained in a ridge waveguide semiconductor optical device in which both sides of a mesa stripe are recessed, for example, into a rectangular shape by a depth not reaching the active layer, wherein the structure that obstructs conductivity is disposed at a portion on the bottom of the rectangular shape. A typical example for the conductivity obstructing structure is attained by a groove or a structure in which impurities are ion implanted into semiconductors.
A typical example of this invention is a semiconductor optical device at least comprising a first cladding layer region of a first conduction type, an active layer region, a second cladding layer region of a second conduction type in a ridged stripe shape formed on the active layer region, a first electrode on the side of the first cladding layer region and a second electrode on the side of the second cladding layer region. Then, semiconductor regions of a desired elongated shape are arranged on both sides of the ridged stripe shape. A recess is formed between the ridged stripe shape region and each of the region of the elongate shape, and a depth of the recess doesn""t reach the active layer region.
The device further has the following three features: (1) At least a portion that obstructs conductivity is provided at a portion of the recess. (2) The second electrode is extended on at least one of the first and the second semiconductor region of the elongated shape.
(3) The distance between each of the sides of the ridged stripe shape region and the portion that obstructs conductivity along the propagating direction of light is 2 xcexcm or more and not exceeding 10 xcexcm.
As a semiconductor optical device according to this invention, a semiconductor laser device is a typical example. In addition, this invention is applicable also to an optical device having an optical waveguide, which should avoid diffusion of carriers in the lateral direction of the active layer region. This example is, for instance, a semiconductor optical modulator. Alternatively, this invention is applicable to a semiconductor integrated optical device in which such semiconductor optical devices are mounted on one substrate.